We propose to examine the binding and uptake of tritiated somatostatin by isolated rat pancreatic islets. Radiolabeled somatostatin will be prepared by reductive methylation using high specific activity sodium borotritide and formaldehyde. Isolated islets will be incubated with labeled somatostatin for intervals of one to thirty minutes, the islets will be washed and fixed with glutaraldehyde and sections prepared for electron microscopic autoradiography. The location and quantitative distribution of developed silver grains on both alpha and beta cells will be determined as a function of glucose concentration and time of incubation. Simultaneous experiments will be carried out to determine the rate of intracellular degradaton of somatostatin by islet cells by homogenizing incubated islets and chromatographing of the acid soluble portion of the homogenate on gel filtration columns equilibrated and eluted with 5% acetic acid.